Wet Chemical Colorimetric Estimation of CO: An Update on the Reduced Silver Sol Spectral and Kinetic Transformations to Silver nanoparticle

Abstract

Measurements of ppm (v/v) level CO_g concentration is conveniently performed by its preconcentration in alkaline absorber solution of Ag⁺-(4)- HCO₂-C₆H₄-SO₂NH₂ complex, followed by a spectral measurement of the reduced silver sol. In this study, the transitory nature of this latter species and its subsequent real-time transformation to silver nanoparticle are presented. These results were based on spectral measurements made under varying concentrations of alkali, (4)-HCO₂-C₆H₄-SO₂NH₂, and Ag⁺ in the absorber solution, and in the presence of a wide range of sampled CO_g concentration. The initially created light yellow colored sol with its broad absorption profile peaking at 380 nm and absorption coefficient 3500 ± 300 cm⁻¹ M⁻¹ (related to the amount of sampled [CO_g] as standardized by gas chromatographic analysis) changed into the characteristic yellow orange nanoparticle with its plasmon band peak absorption at 425 nm and absorption coefficient 6350 ± 300 cm⁻¹ M⁻¹. Under different sampling conditions, the respective first-order conversion rates varied between 0.03 and 0.15 h⁻¹, whereas simultaneous dynamic light scattering measurements revealed steady growth of the averaged particle size ranging from 60 to 300 nm.